Biofuel co-products as livestock feed - Opportunities and challenges

Biofuels: their co-products and water impacts in the context of life-cycle analysis 485FIGURE 2System boundary of life-cycle analysis of sugar cane ethanolEnergy inputsfor farmingCO 2viaPhotosynthesisCO 2in theAtmosphereCO 2emissionsDuring fermentationCO 2emissionsfrom BagassecombustionCO 2emissionsfrom ethanolcombustionFertilizerEthanoltransportto U.S.DomesticEthanoldistributionN 2O emissionsfrom soil andwater streamsDirectland-usechangeChange in soil carbonEffective viaprice signalIndirect land-usechanges for other cropsand in other regionsBagasseConventionalelectricitygenerationDisplacementSteam and/or Powerresidue and dedicated energy crops (switchgrass,miscanthus and various other plants). Figure 3 sketchesthe life cycle of ethanol from switchgrass. Conversiontechnologies for these feedstocks are at pilot-plant scalenow, and research and development activities aboundin China, the EU and the United States (e.g. Feng etal., 2011; Scordia et al., 2011). Because commercialscalelignocellulosic facilities are in development, technoeconomicanalyses and LCAs of this technology are basedon process models, such as those produced by the NationalRenewable Energy Laboratory (Humbird et al., 2011). Ingeneral, prior to fermentation, cellulosic feedstocks mustundergo a chemical, thermal or biological pre-treatmentstep to release sugars from biomass and separate lignin.The subsequent fermentation step converts the sugarsto ethanol. Combustion of lignin can fuel on-site steamand power generation. As with sugar cane ethanol plants,this on-site power can be used at the plant and possiblyexported to the grid. This ability of second-generationbiofuels to produce power as a co-product is an attractivecharacteristic. Further, feedstocks such as maize stoverand forest residues do not compete directly with foodproduction. Feedstocks such as dedicated energy cropspose less competition with food production than do grainsand oilseeds as biofuel feedstocks.Third-generation biofuels include biodiesel and renewablediesel from algae, and other hydrocarbon fuels similarto gasoline and diesel (sometimes called drop-in fuels)from cellulosic biomass via gasification, pyrolysis andhydro-liquefaction. Significant research and developmentefforts are underway to develop technologies for thesethird-generation biofuels. Besides biofuels from algal oil,algal feedstocks can provide significant amounts of biomassfor methane production via anaerobic digesters. Thebio-methane can be further used for electricity production.Production of hydrocarbon fuels from biomass can co-produceother energy products such as electricity and fuel gas.MARKET POTENTIAL OF BIOFUEL CO-PRODUCTSAs noted above, the production of starch and lignocellulosicethanol results in the generation of several co-products.This section discusses co-products from these pathways, aswell as co-products generated from soybean and rapeseedderivedbiodiesel. Table 1 catalogues co-products yields invarious selected biofuels pathways analysed by ArgonneNational Laboratory (2010).ANIMAL FEED BY-PRODUCTS OF MAIZE STARCHETHANOL MANUFACTURINGAs discussed above, DGS, used as animal feed, is a co-productat dry-mill ethanol plants. A plant’s decision to produceWDGS or DDGS must weigh the competing costs of theenergy to dry DGS to make DDGS against the shorter shelflife and increased transportation costs of heavier WDGS,